Electronic unit and power feeding system

ABSTRACT

An electronic unit includes: an electricity reception section configured to receive power fed from a power feeding unit using a magnetic field; a voltage detection section configured to detect a received voltage supplied from the electricity reception section; and a control section, wherein while preliminary power feeding at a lower power than main power feeding is performed from the power feeding unit, and when a received voltage detected by the voltage detection section is equal to or higher than a predetermined threshold voltage, the control section performs voltage reduction control so as to decrease the received voltage to lower than the threshold voltage.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Priority PatentApplication JP 2013-80430 filed Apr. 8, 2013, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a power feeding system that performspower supply (power feeding, electricity transmission, or powertransmission) in a noncontact manner to an objective unit such as anelectronic unit, and to an electronic unit applicable to such a powerfeeding system.

Recently, a power feeding system (a noncontact power feeding system or awireless charging system), which supplies power in a noncontact mannerto consumer electronics (CE) devices such as a mobile phone and aportable music player, is the subject of interest. Such a noncontactpower feeding system makes it possible to start charge only by placingan electronic unit (a secondary unit) on a charge tray (a primary unit)instead of starting charge by inserting (connecting) a connector of apower supply unit, such as an AC adaptor, into a unit. In other words,such a system eliminates necessity of terminal connection between theelectronic unit and the charge tray.

A method of performing such noncontact power supply is roughlyclassified into two techniques. A first technique is a widely known,electromagnetic induction method capable of efficient power feeding dueto its extremely high coupling degree between an electricitytransmission side (primary side) and an electricity reception side(secondary side). A second technique is a so-called magnetic resonancemethod that is characterized in that a small amount of magnetic flux maybe satisfactorily shared by the electricity transmission side and theelectricity reception side by actively using a resonant phenomenon.

In recent years, the trend of standardization has been developing, andstandardization is actively advanced mainly by an industry group namedWireless Power Consortium (WPC). The standardization enablescompatibility between products of different enterprises, and enablescharge in many combinations of primary units and secondary units. Forexample, Japanese Unexamined Patent Application Publication Nos.2001-102974, 2008-206233, 2002-34169, 2005-110399, and 2010-63245, andInternational Patent Application WO 00/27531 each disclose such anoncontact power feeding system.

SUMMARY

Such a noncontact power feeding system is being further investigated toachieve a noncontact feeding system of higher power. It is thereforedesired to propose a technique that makes it possible to appropriatelyperform control during power feeding using a magnetic field.

It is desirable to provide an electronic unit and a power feeding systemcapable of appropriately performing control during power feeding using amagnetic field.

According to an embodiment of the present disclosure, there is providedan electronic unit, including: an electricity reception sectionconfigured to receive power fed from a power feeding unit using amagnetic field; a voltage detection section configured to detect areceived voltage supplied from the electricity reception section; and acontrol section, wherein while preliminary power feeding at a lowerpower than main power feeding is performed from the power feeding unit,and when a received voltage detected by the voltage detection section isequal to or higher than a predetermined threshold voltage, the controlsection performs voltage reduction control so as to decrease thereceived voltage to lower than the threshold voltage.

According to an embodiment of the present disclosure, there is provideda power feeding system, including: one or more electronic units; and apower feeding unit configured to perform power feeding to the electronicunit using a magnetic field, wherein the electronic unit includes anelectricity reception section that receives power fed from the powerfeeding unit, a voltage detection section that detects a receivedvoltage supplied from the electricity reception section, and a controlsection, wherein while preliminary power feeding at a lower power thanmain power feeding is performed from the power feeding unit, and when areceived voltage detected by the voltage detection section is equal toor higher than a predetermined threshold voltage, the control sectionperforms voltage reduction control so as to decrease the receivedvoltage to lower than the threshold voltage.

In the electronic unit and the power feeding system according to theabove-described respective embodiments of the present disclosure, when areceived voltage, which is detected during preliminary power feedingfrom the power feeding unit, is equal to or higher than thepredetermined threshold voltage, voltage reduction control is performedso as to decrease the received voltage to lower than the thresholdvoltage. Consequently, the received voltage is avoided from excessivelyincreasing during subsequent main power feeding (at higher power thanthe preliminary power feeding).

According to the electronic unit and the power feeding system of theabove-described respective embodiments of the present disclosure, when areceived voltage, which is detected during preliminary power feedingfrom the power feeding unit, is equal to or higher than thepredetermined threshold voltage, voltage reduction control is performedso as to decrease the received voltage to lower than the thresholdvoltage. As a result, the received voltage is allowed to be avoided fromexcessively increasing during subsequent main power feeding.Consequently, it is possible to perform appropriate control during powerfeeding using a magnetic field.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the technology as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated in and constitutea part of this specification. The drawings illustrate embodiments and,together with the specification, serve to explain the principles of thetechnology.

FIG. 1 is a perspective diagram illustrating an exemplary appearanceconfiguration of a power feeding system according to an exampleembodiment of the present disclosure.

FIG. 2 is a diagram illustrating an exemplary detailed configuration ofthe power feeding system illustrated in FIG. 1.

FIG. 3 is a circuit diagram illustrating an exemplary detailedconfiguration of an AC signal generation circuit illustrated in FIG. 2.

FIG. 4 is a timing waveform diagram illustrating an exemplary controlsignal for the AC signal generation circuit.

FIG. 5A is a circuit diagram schematically illustrating an exemplaryoperation of the AC signal generation circuit illustrated in FIG. 3.

FIG. 5B is a circuit diagram schematically illustrating anotherexemplary operation of the AC signal generation circuit illustrated inFIG. 3.

FIG. 6 is a circuit diagram illustrating an exemplary detailedconfiguration of a dummy load circuit illustrated in FIG. 2.

FIG. 7 is a circuit diagram schematically illustrating an exemplarystate of the dummy load circuit illustrated in FIG. 6.

FIG. 8 is a circuit diagram illustrating a configuration of a powerfeeding unit according to a comparative example 1.

FIG. 9 is a table for explaining loss in a DC/DC converter illustratedin FIG. 8.

FIG. 10 is a flowchart illustrating power feeding operation and chargeoperation according to a comparative example 2.

FIG. 11 is a flowchart illustrating power feeding operation and chargeoperation according to a comparative example 3.

FIG. 12 is a flowchart illustrating an exemplary power feeding operationand charge operation according to the example embodiment.

FIG. 13 is a diagram illustrating an exemplary operation state duringpreliminary power feeding.

FIG. 14 is a diagram illustrating an exemplary relationship between areceived voltage and a dummy load.

FIG. 15 is a circuit diagram schematically illustrating anotherexemplary state of the dummy load circuit illustrated in FIG. 6.

FIG. 16A is a circuit diagram schematically illustrating anotherexemplary state of the dummy load circuit illustrated in FIG. 6.

FIG. 16B is a circuit diagram schematically illustrating anotherexemplary state of the dummy load circuit illustrated in FIG. 6.

FIG. 17 is a diagram illustrating an exemplary relationship between areceived voltage and a dummy load in Modification 1.

FIG. 18 is a diagram illustrating an exemplary configuration of a powerfeeding system according to Modification 2.

DETAILED DESCRIPTION

Hereinafter, an embodiment of the present disclosure is described indetail with reference to the accompanying drawings. It is to be notedthat description is made in the following order.

1. Embodiment (Example of a case where a received voltage is decreasedusing a dummy load).

2. Modifications

Modification 1 (Example of selectively using a plurality of types ofdummy loads in accordance with a level of a received voltage).

Modification 2 (Example of decreasing a received voltage by controllinga load current).

3. Other Modifications

EMBODIMENT Overall Configuration of Power Feeding System 4

FIG. 1 illustrates an exemplary appearance configuration of a powerfeeding system (power feeding system 4) according to an embodiment ofthe present disclosure. FIG. 2 is a block diagram as a circuit diagramthat illustrates an exemplary detailed configuration of the powerfeeding system 4. The power feeding system 4 is a system (noncontactpower feeding system) that performs power transmission (power supply,power feeding, or electricity transmission) in a noncontact manner usinga magnetic field (using magnetic resonance, electromagnetic induction,or the like; the same holds true hereinafter). The power feeding system4 includes a power feeding unit 1 (primary unit) and one or moreelectronic units (here, one electronic unit 2; a secondary unit) as anobjective unit of power feeding.

In the power feeding system 4, for example, as illustrated in FIG. 1,the electronic unit 2 is placed on (or disposed close to) a powerfeeding surface (an electricity transmission surface) S1 of the powerfeeding unit 1, thereby power transmission is performed from the powerfeeding unit 1 to the electronic unit 2. In this exemplary case, thepower feeding unit 1 is in a mat shape (tray shape), in which area ofthe power feeding surface S1 is larger than area of the electronic unit2 as a power feeding object, etc.

(Power Feeding Unit 1)

As described above, the power feeding unit 1 is a unit (charge tray)configured to feed power to the electronic unit 2 using a magneticfield. For example, as illustrated in FIG. 2, the power feeding unit 1may include an electricity transmission section 10, an AC signalgeneration circuit (an AC signal generation section or a high-frequencypower generation circuit) 11, a communication section 12, and a controlsection 13.

The electricity transmission section 10 includes an electricitytransmission coil (a primary coil) L1, a capacitor C1 (resonancecapacitor), and the like. Such an electricity transmission coil L1 and acapacitor C1 are electrically connected in series to each other.Specifically, a first end of the electricity transmission coil L1 isconnected to a first end of the capacitor C1, a second end of theelectricity transmission coil L1 is grounded, and a second end of thecapacitor C1 is connected to an output terminal of the AC signalgeneration circuit 11. The electricity transmission section 10 uses suchan electricity transmission coil L1 and a capacitor C1 to feed power tothe electronic unit 2 (in detail, an electricity reception section 20described later) using an AC magnetic field (see an arrow P1 in FIG. 2).Specifically, the electricity transmission section 10 has a function ofradiating a magnetic field (magnetic flux) from the power feedingsurface S1 to the electronic unit 2.

The electricity transmission section 10 includes an LC resonance circuitthat is configured of the electricity transmission coil L1 and thecapacitor C1. The LC resonance circuit formed in the electricitytransmission section 10 and an LC resonance circuit formed in theelectricity reception section 20 described later are designed to bemagnetically coupled to each other (mutual induction).

For example, the AC signal generation circuit 11 may be a circuitconfigured to use power (a DC signal Sdc) supplied from an externalpower supply 9 (a parent power supply) of the power feeding unit 1 togenerate a predetermined AC signal Sac (high-frequency power) forperforming power feeding. The AC signal Sac is supplied to theelectricity transmission section 10. Examples of the external powersupply 9 may include a typical AC adaptor, and a power supply (powersupplying capability: 500 mA and a power voltage: about 5V) of universalserial bus (USB) 2.0 provided in a personal computer (PC), etc.

For example, as described later, such an AC signal generation circuit 11may be configured of a switching amplifier (so-called a class Eamplifier, a differential amplifier, or the like) containing one or moreswitching elements SW1 configured of metal oxide semiconductor (MOS)transistors, or the like. The switching element SW1 is configured toreceive control signals CTL1 for power feeding from the control section13. The configuration of the AC signal generation circuit 11 isdescribed in detail later.

The communication section 12 is configured to mutually performpredetermined communication operation with a communication section 26described later in the electronic unit 2 (see an arrow C1 in FIG. 2).

The control section 13 is configured to perform various types of controloperation in the power feeding unit 1 as a whole (or the power feedingsystem 4 as a whole). Specifically, the control section 13 performscontrol of electricity transmission operation of the electricitytransmission section 10 and control of communication operation of thecommunication section 12. In addition, for example, the control section13 may have a function of optimization control of power to be fed, anauthentication function of an objective unit of power feeding, afunction of detecting a proximate objective unit of power feeding, and afunction of detecting contamination of a dissimilar metal, etc. In theabove-described control of electricity transmission operation, thecontrol section 13 uses the above-described control signals CTL1 tocontrol operation of the AC signal generation circuit 11. For example,such a control section 13 may be configured of a microcomputer, a pulsegenerator, and the like. The operation of controlling the AC signalgeneration circuit 11 by the control section 13 is described in detaillater.

(Electronic Unit 2)

For example, the electronic unit 2 may be a standalone electronic unittypified by a television receiver, a portable electronic unit containinga battery typified by a mobile phone and a digital camera, etc. Forexample, as illustrated in FIG. 2, the electronic unit 2 includes theelectricity reception section 20, a rectifier circuit 21, a voltagedetection section 22, a dummy load circuit 23, a charge section 24, abattery 25, a communication section 26, a control section 27, and amemory section 28. The dummy load circuit 23 corresponds to a specificbut not limitative example of “voltage reduction section” in oneembodiment of the present disclosure.

The electricity reception section 20 includes an electricity receptioncoil (secondary coil) L2, capacitors C2 s and C2 p (resonancecapacitors), and the like. The electricity reception coil L2 and thecapacitor C2 s are electrically connected in series to each other, whilethe electricity reception coil L2 and the capacitor C2 p areelectrically connected in parallel to each other. Specifically, a firstend of the capacitor C2 s is connected to a first input terminal of therectifier circuit 21 and a first end of the capacitor C2 p, while asecond end of the capacitor C2 s is connected to a first end of theelectricity reception coil L2. A second end of the electricity receptioncoil L2 is connected to a second input terminal of the rectifier circuit21 and a second end of the capacitor C2 p. The electricity receptionsection 20 has a function of using the electricity reception coil L2,the capacitors C2 s and C2 p, and the like to receive power (fed power)transmitted from the electricity transmission section 10 in the powerfeeding unit 1.

The electricity reception section 20 includes an LC resonance circuitthat is configured of the electricity reception coil L2 and thecapacitors C2 s and C2 p. As described before, the LC resonance circuitformed in the electricity reception section 20 is magnetically coupledwith the LC resonance circuit formed in the electricity transmissionsection 10. Consequently, LC resonance operation is performed at aresonance frequency that is substantially equal to a frequency of thehigh-frequency power (AC signal Sac) generated by the AC signalgeneration circuit 11.

The rectifier circuit 21 is a circuit configured to rectify a receivedvoltage (AC voltage) supplied from the electricity reception section 20to generate a DC voltage. In other words, the rectifier circuit 21rectifies an AC received voltage (AC received voltage Vac) supplied fromthe electricity reception section 20 to generate a DC received voltage(DC received voltage Vdc). For example, the rectifier circuit 21 may bea circuit in a bridge configuration including a plurality of rectifierelements (diodes). For example, the rectifier circuit 21 may be asynchronous rectifier circuit including transistors.

The voltage detection section 22 is configured to detect the receivedvoltage supplied from the electricity reception section 20. Inparticular, in this exemplary case, the voltage detection section 22detects the received voltage (DC received voltage Vdc), which has beenrectified by the rectifier circuit 21, on a downstream side of therectifier circuit 21 on a power supply line Lp. The DC received voltageVdc detected in this way is output to the control section 27. Forexample, such a voltage detection section 22 may be configured of aresistance voltage divider, an analog to digital converter (ADC), or thelike.

The dummy load circuit 23 is disposed between the rectifier circuit 21and the charge section 24 on the power supply line Lp, and may includeone or more dummy loads (dummy resistances, etc.). When a predeterminedcondition described later is satisfied, the dummy load circuit 23performs operation (voltage reduction operation) of decreasing thereceived voltage (the DC received voltage Vdc in this exemplary case) inaccordance with control (a control signal CTL2) from the control section27. The configuration of the dummy load circuit 23 and the voltagereduction operation are described in detail later.

The charge section 24 is configured to perform operation of charging thebattery 25 as a main load based on the DC power output from therectifier circuit 21.

The battery 25 is configured to store power in accordance with thecharge operation of the charge section 24, and may be configured of abattery (secondary battery) such as, for example, a lithium ion battery.

The communication section 26 is configured to mutually perform theabove-described predetermined communication operation with thecommunication section 12 in the power feeding unit 1 (see the arrow C1in FIG. 2).

The control section 27 is configured to perform various types of controloperation in the electronic unit 2 as a whole (or power feeding system 4as a whole). Specifically, the control section 24 performs control ofelectricity reception operation of the electricity reception section 20and control of the communication operation of the communication section26. In addition, for example, the control section 24 may have a functionof optimization control of power to be received, and a function ofcontrolling the charge operation of the charge section 24.

In this embodiment, while preliminary power feeding at a lower powerthan the main power feeding is performed from the power feeding unit 1(at start operation), and when the received voltage (DC received voltageVdc) detected by the voltage detection section 22 is equal to or higherthan a predetermined threshold voltage Vth (Vdc≧Vth), the controlsection 27 performs the following voltage reduction control.Specifically, in such a case, the control section 27 performs thevoltage reduction control such that the DC received voltage Vdc isdecreased to lower than the threshold voltage Vth (Vdc<Vth). Morespecifically, for example, the control section 27 may use one or more ofthe dummy loads in the above-described dummy load circuit 23 to performsuch voltage reduction control. For example, such a control section 27may be configured of a microcomputer, etc. The voltage reduction controloperation of the control section 27 is described in detail later.

The memory section 28 is configured to store the various types ofinformation that are to be used by the control section 27. Specifically,for example, the memory section 28 stores information of theabove-described threshold voltage Vth, etc.

[Exemplary Detailed Configuration of AC Signal Generation Circuit 11]

An exemplary detailed configuration of the above-described AC signalgeneration circuit 11 is now described with reference to FIGS. 3, 4, 5Aand 5B. FIG. 3 illustrates an exemplary circuit configuration of the ACsignal generation circuit 11 together with an external power supply 9,the electricity transmission section 10, and the control section 13.

In this exemplary case, the AC signal generation circuit 11 has a bridgecircuit configuration using four switching elements SW1 a, SW1 b, SW1 c,and SW1 d as the above-described switching elements SW1. In thisexemplary case, such switching elements SW1 a, SW1 b, SW1 c, and SW1 dare each configured of a MOS transistor. In the AC signal generationcircuit 11, the respective gates of the switching elements SW1 a, SW1 b,SW1 c, and SW1 d independently receive control signals CTL1 a, CTL1 b,CTL1 c, and CTL1 d, respectively, as the above-described control signalsCTL1. Sources of the switching element SW1 a and SW1 c are eachconnected to a connection line from the external power supply 9. A drainof the switching element SW1 a is connected to a drain of the switchingelement SW1 b, and a drain of the switching element SW1 c is connectedto a drain of the switching element SW1 d. Sources of the switchingelements SW1 b and SW1 d are each connected to ground (earth). Thedrains of the switching elements SW1 a and SW1 b are each connected to afirst end of the capacitor C1 in the electricity transmission section10, and the drains of the switching element SW1 c and SW1 d are eachconnected to a first end of the electricity transmission coil L1 in theelectricity transmission section 10.

For example, as illustrated in FIG. 4, the control signals CTL1 (CTL1 a,CTL1 b, CTL1 c, and CTL1 d) are each a pulse signal having apredetermined frequency f (CTL1(f)=f1) and a predetermined duty ratioDuty (CTL1(Duty)=10%, 50%, or the like). As illustrated in FIG. 4, pulsewidth modulation (PWM) is performed through control of the duty ratioDuty of each control signal CTL1.

According to such a configuration, in the AC signal generation circuit11, the switching elements SW1 a, SW1 b, SW1 c, and SW1 d perform ON/OFFoperation (switching operation at the frequency f and the duty ratioDuty) in accordance with the control signals CTL1 a, CTL1 b, CTL1 c, andCTL1 d, respectively. Specifically, ON/OFF operation of the switchingelement SW1 is controlled using the control signals CTL1 supplied fromthe control section 13. Consequently, for example, the AC signal Sac isgenerated based on the DC signal Sdc received from the external powersupply 9, and is supplied to the electricity transmission section 10.

In the AC signal generation circuit 11, a circuit configuration isswitchable as below between a full-bridge circuit and a half-bridgecircuit in accordance with the control signals CTL1 a, CTL1 b, CTL1 c,and CTL1 d. Consequently, a voltage is allowed to be varied during powerfeeding in accordance with control of switching operation withoutvarying a hardware configuration.

Specifically, for example, as illustrated in FIG. 5A, when the fourswitching elements SW1 a, SW1 b, SW1 c, and SW1 d each perform ON/OFFoperation, the circuit has a configuration of the full-bridge circuit.

For example, as illustrated in FIG. 5B, when the two switching elementsSW1 a and SW1 b each perform ON/OFF operation, the switching element SW1c is continuously OFF, and the switching element SW1 d is continuouslyON, the circuit configuration is as follows. Specifically, in this case,the circuit configuration is equivalent to a half-bridge circuitconfigured of the two switching elements SW1 a and SW1 b. Consequently,in this case, a voltage (voltage to be fed) generated by the AC signalgeneration circuit 11 during power feeding is about half the voltagegenerated in case of the full-bridge circuit illustrated in FIG. 5A. InFIGS. 5A and 5B and subsequent similar drawings, each switching elementis schematically shown in a form of a switch in order to facilitateunderstanding of an operation state thereof.

[Exemplary Detailed Configuration of Dummy Load Circuit 23]

An exemplary detailed configuration of the above-described dummy loadcircuit 23 is now described with reference to FIGS. 6 and 7. FIG. 6illustrates an exemplary detailed configuration of the dummy loadcircuit 23 together with the control section 27.

In this exemplary case, the dummy load circuit 23 includes two dummyloads Ra and Rb configured of resistance elements (dummy resistances),and two switching elements SW2 a and SW2 b configured of MOStransistors. The dummy load Ra and the switching element SW2 a areconnected in series to each other between the power supply line Lp and aground line, and the dummy load Rb and the switching element SW2 b areconnected in series to each other between the power supply line Lp andthe ground line. Specifically, a first end of the dummy load Ra isconnected to the power supply line Lp, a second end of the dummy load Rais connected to the drain of the switching element SW1 a, and a sourceof the switching element SW1 a is connected to the ground line.Similarly, a first end of the dummy load Rb is connected to the powersupply line Lp, a second end of the dummy load Rb is connected to thedrain of the switching element SW1 b, and a source of the switchingelement SW1 b is connected to the ground line. Such an element pair ofthe dummy load Ra and the switching element SW1 a and an element pair ofthe dummy load Rb and the switching element SW1 b are disposed inparallel to each other. The gates of the switching elements SW2 a andSW2 b independently receive the control signals CTL2 a and CTL2 b,respectively, as the above-described control signals CTL2.

According to such a configuration, the dummy load circuit 23 is set suchthat the two switching elements SW2 a and SW2 b are independently ON orOFF in accordance with the control signals CTL2 a and CTL2 b suppliedfrom the control section 27. As a result, the dummy load circuit 23 isconfigured such that the two dummy loads Ra and Rb are independentlyconnected or disconnected between supply lines of the DC receivedvoltage Vdc (between the power supply line Lp and a ground line).

For example, as illustrated in FIG. 7, the dummy load circuit 23 is setsuch that both the switching elements SW2 a and SW2 b are OFF duringnormal operation (in any case other than the case of satisfying(Vdc≧Vth) as described later). Specifically, the dummy load circuit 23is set such that both the dummy loads Ra and Rb are disconnected betweenthe supply lines of the DC received voltage Vdc.

[Functions and Effects of Power Feeding System 4] (1. Summary of OverallOperation)

In the power feeding system 4, the AC signal generation circuit 11 inthe power feeding unit 1 supplies predetermined high-frequency power (anAC signal Sac) for electricity transmission to the electricitytransmission coil L1 and the capacitor C1 in the electricitytransmission section 10 based on power supplied from the external powersupply 9. Consequently, the electricity transmission coil L1 in theelectricity transmission section 10 generates a magnetic field (magneticflux). At this time, when the electronic unit 2 as an objective unit ofpower feeding is placed on (or disposed close to) a top (the powerfeeding surface S1) of the power feeding unit 1, the electricitytransmission coil L1 in the power feeding unit 1 becomes proximate tothe electricity reception coil L2 in the electronic unit 2 in thevicinity of the power feeding surface S1.

In this way, when the electricity reception coil L2 is disposed close tothe electricity transmission coil L1 generating a magnetic field,electromotive force (induced electromotive force) is induced in theelectricity reception coil L2 by the magnetic flux generated from theelectricity transmission coil L1. In other words, the magnetic field isgenerated by electromagnetic induction or magnetic resonance whileinterlinking with each of the electricity transmission coil L1 and theelectricity reception coil L2. Consequently, power is transmitted fromthe electricity transmission coil L1 side (the primary side, the powerfeeding unit 1 side, or the electricity transmission section 10 side) tothe electricity reception coil L2 side (the secondary side, theelectronic unit 2 side, or the electricity reception section 20 side)(see the arrow P1 in FIG. 2). At this time, the electricity transmissioncoil L1 in the power feeding unit 1 is magnetically coupled with theelectricity reception coil L2 in the electronic unit 2, leading to LCresonance operation.

In the electronic unit 2, the AC power received by the electricityreception coil L2 is then supplied to the charge section 24 via therectifier circuit 21, and, for example, the following charge operationmay be performed. Specifically, an AC voltage (AC current) is convertedinto a predetermined DC voltage (DC current) by the rectifier circuit21, and then the charge section 24 charges the battery 25 based on theDC voltage. In this way, in the electronic unit 2, charge operation isperformed based on the power received by the electricity receptionsection 20.

In other words, this embodiment eliminates necessity of terminalconnection to, for example, an AC adaptor during charge of theelectronic unit 2, and thus makes it possible to easily start chargeonly by placing the electronic unit 2 on (or disposing the electronicunit 2 close to) the power feeding surface S1 of the power feeding unit1 (i.e., allows noncontact power feeding). This leads to reduction inwork of a user.

During such operation, mutual communication operation is performedbetween the communication section 12 in the power feeding unit 1 and thecommunication section 26 in the electronic unit 2 (see the arrow C1 inFIG. 2). For example, mutual authentication between the units, controlof power feeding efficiency, and the like may be performed through suchmutual communication operation.

(2. Reduction Operation of Received Voltage)

Such a noncontact power feeding system is being further investigated toachieve a noncontact feeding system of higher power. In most of thecommercially available, noncontact power feeding systems at present, thepower to be received is 1 W, 2.5 W, or 5 W, and is promisingly increasedto 10 W or 15 W in future. Therefore, an issue of downward compatibilityoccurs. Specifically, the primary unit is necessary to cover a widepower range in correspondence to power requested by the secondary unit.In addition, an appropriate power feeding voltage is necessary to be setin the primary side in order to cover such a wide power range. This isbecause the voltage (received voltage) in the secondary side may benecessarily increased in light of heat generation in the coil.

Comparative Example 1

In a power feeding unit 101 according to a comparative example 1illustrated in FIG. 8, therefore, a DC/DC converter 102 is provided in aprimary unit (a power feeding unit 101) and is used to adjust a voltageto be fed. The power feeding unit 101 corresponds to an alteration ofthe power feeding unit 1, in which the DC/DC converter 102 is providedbetween the external power supply 9 and the AC signal generation circuit11, and a control section 103 provided in place of the control section13 controls operation of the DC/DC converter 102.

The power feeding unit 101 controls a voltage to be fed through controlof a voltage, which is to be sent to the AC signal generation circuit11, by the DC/DC converter 102. For example, when power requested by thesecondary unit is small compared with a source voltage of the externalpower supply 9, the DC/DC converter 102 lowers the source voltage, andoutputs the lowered voltage.

The technique of the comparative example 1, however, inevitably causespower loss in the DC/DC converter 102, while the technique gives a widevoltage adjustment range from the source voltage to a lowest outputvoltage of the DC/DC converter 102.

Specifically, for example, power loss in the DC/DC converter 102 is asshown in a table of FIG. 9. In the table, necessary power to be fedcorresponds to the sum of necessary power to be received and power lossin the power feeding system as a whole due to the noncontact powerfeeding. In the noncontact power feeding system, power loss mainlyoccurs in each of an electricity reception circuit containing arectifier circuit, etc., an electricity transmission circuit using a MOStransistor, etc., and a coil. Hence, even if the power feeding system asa whole has an efficiency of 80%, and even if the DC/DC converter 102has an efficiency of 90%, as illustrated in FIG. 9, when power to bereceived is, for example, 10 W or higher, power loss of 1 W or highermay occur in the DC/DC converter 102.

In the power feeding unit 1 of this embodiment, therefore, asillustrated in FIG. 3, no DC/DC converter is provided between theexternal power supply 9 and the AC signal generation circuit 11. Asillustrated in FIGS. 5A and 5B, in the AC signal generation circuit 11,the circuit configuration is allowed to be switched between thefull-bridge circuit and the half-bridge circuit in accordance with thecontrol signals CTL1 a, CTL1 b, CTL1 c, and CTL1 d. As a result, it ispossible to vary a voltage during power feeding in correspondence tocontrol of switching operation without varying a hardware configuration.Specifically, for example, when the necessary power to be fed is low(for example, 5 W or lower), the circuit configuration may be set to thehalf-bridge circuit. When the necessary power to be fed is high (forexample, 10 W or higher), the circuit configuration is switched to thefull-bridge circuit. As a result, it is possible to supply anappropriate voltage to be fed. Moreover, omission of the DC/DC converter102 improves efficiency compared with the comparative example 1.

This technique, however, has an important issue of switching timing ofthe circuit configuration of the AC signal generation circuit 11(increasing timing of the power to be fed and the voltage to be fed).Specifically, for example, difficulties of comparative examples 2 and 3described below may occur depending on such timing.

Comparative Example 2

FIG. 10 is a flowchart illustrating power feeding operation and chargeoperation according to the comparative example 2. In the power feedingoperation and charge operation of the comparative example 2, first,preliminary power feeding at a lower power than main power feedingdescribed later is started from the primary unit to the secondary unit(step S901 in FIG. 10). The secondary unit is then started using thepower received through the preliminary power feeding (step S902). Insuch preliminary power feeding, since the necessary power to be fed islower than in the main power feeding, the AC signal generation circuit11 in the primary unit is set to the half-bridge circuit.

Subsequently, the secondary unit determines power to be received duringthe main power feeding through communication between the primary unitand the secondary unit (step S903). The secondary unit then informs,using the communication, the primary unit of a start request of mainpower feeding (step S904).

Subsequently, the main power feeding at a higher power than thepreliminary power feeding is started from the primary unit to thesecondary unit (step S905). In other words, in the main power feeding,since the necessary power to be fed is higher than in the preliminarypower feeding, the AC signal generation circuit 11 in the primary unitis switched from the half-bridge circuit to the full-bridge circuit.

Subsequently, a main load (the battery, etc.) is set to a connectionstate in the secondary unit (step S906), and operation of charging thebattery is performed based on the received power in the secondary unit(step S907). This is the end of the power feeding operation and chargeoperation illustrated in FIG. 10.

Thus, in the power feeding operation and charge operation of thecomparative example 2, the circuit configuration of the AC signalgeneration circuit 11 in the primary unit is switched (the power to befed is controlled to be increased) before connection of the main load inthe secondary unit. In the comparative example 2, therefore, thefollowing issue may occur at timing indicated by an arrow P201 in FIG.10. Specifically, when the circuit configuration is switched (the powerto be fed is controlled to be increased) before connection of the mainload, the received voltage is increased about two times in a no-loadstate; hence, an excessively high received voltage may be caused in caseof a high coupling coefficient between the electricity transmission coiland the electricity reception coil. Such an excessively high receivedvoltage may result in breakage of an integrated circuit (IC) and thelike in the secondary unit. If an element withstanding voltage(withstanding voltage of an integrated circuit (IC), etc.) in thesecondary unit is designed to be high, no issue occurs. In such a case,however, manufacturing cost may increase, or may be disadvantageouslyincreased in size.

Comparative Example 3

On the other hand, FIG. 11 is a flowchart illustrating power feedingoperation and charge operation according to the comparative example 3.The power feeding operation and charge operation of the comparativeexample 3 corresponds to an alteration of the power feeding operationand charge operation of the comparative example 2, in which connectionof the main load in the secondary unit (step S906) is performed beforeinformation of a start request of main power feeding (step S904) andstart of main power feeding (step S905). In other words, in thecomparative example 3, the circuit configuration of the AC signalgeneration circuit 11 in the primary unit is switched (the power to befed is controlled to be increased) after connection of the main load inthe secondary unit, contrary to the comparative example 2.

In the comparative example 3, however, the following issue may newlyoccur at timing indicated by an arrow P301 in FIG. 11. Specifically, inthis case, since the main load is connected (a current is drawn to amain load side) before power to be fed is increased, received voltagemay be extremely decreased, so that ICs in the secondary unit may bedisabled.

Thus, in the noncontact power feeding system, since the couplingcoefficient is not constant depending on the situation during powerfeeding, etc., switching timing of the circuit configuration of the ACsignal generation circuit 11 (increasing timing of the power to be fedand the voltage to be fed) is difficult to be determined. In a possibletechnique, the circuit configuration of the power feeding system as awhole is switched at a certain timing. In this case, however, each ofthe primary unit and the secondary unit is necessary to have a timer. Inaddition, disadvantageous delay may actually occur due to communication.Moreover, such a switching technique may not be necessarily performed atany time in the primary unit. Hence, the secondary unit may necessarilyhave a mechanism that prevents any trouble even if its circuitconfiguration is switched.

Embodiment

This embodiment, therefore, solves the above-described issues in theelectronic unit 2 as the secondary unit in the following manner.

Specifically, while preliminary power feeding at a lower power than themain power feeding is performed from the power feeding unit 1, and whenthe DC received voltage Vdc detected by the voltage detection section 22is equal to or higher than a predetermined threshold voltage Vth(Vdc≧Vth), the control section 27 in the electronic unit 2 performs thefollowing voltage reduction control. Specifically, in such a case, thecontrol section 27 performs the voltage reduction control such that theDC received voltage Vdc is decreased to lower than the threshold voltageVth (Vdc<Vth). More specifically, the control section 27 may use one ormore of the dummy loads in the dummy load circuit 23 to perform suchvoltage reduction control. A series of power feeding operation andcharge operation containing such voltage reduction control is nowdescribed in detail.

FIG. 12 is a flowchart illustrating power feeding operation and chargeoperation of this embodiment. In this power feeding operation and chargeoperation, first, preliminary power feeding at a lower power than themain power feeding is started from the power feeding unit 1 to theelectronic unit 2 (step S101 in FIG. 12). The electronic unit 2 is thenstarted using the power received through the preliminary power feeding(step S102).

Subsequently, the electronic unit 2 (control section 27) determinespower to be received during the main power feeding through communicationbetween the primary unit and the secondary unit (step S103). In thepreliminary power feeding, since the necessary power to be fed is lowerthan that in the main power feeding, the AC signal generation circuit 11in the power feeding unit 1 is set to the half-bridge circuit, as withthe above-described comparative examples 2 and 3.

In such preliminary power feeding, for example, as illustrated in FIG.13, the control section 27 controls the charge section 24 to be in anon-operation state, thereby the main load (the battery 25 in thisexemplary case) is set to be disconnected from the power supply line Lp.

Subsequently, the voltage detection section 22 in the electronic unit 2detects the DC received voltage Vdc given in the preliminary powerfeeding (step S104), and then informs the power feeding unit 1 of astart request of the main power feeding based on the power to bereceived determined in step S103 (step S106 described later). Thecontrol section 27 then determines whether the detected DC receivedvoltage Vdc is lower than the predetermined threshold voltage Vth(Vdc<Vth) or not (step S105).

For example, as illustrated in FIG. 14, the threshold voltage Vth is setto a value that is less than half the value of an element withstandingvoltage Vb in the electronic unit 2 (Vth<(Vdc/2)). This is because whenthe circuit configuration of the AC signal generation circuit 11 isswitched from the half-bridge circuit to the full-bridge circuit asdescribed above, the value of the received voltage (DC received voltageVdc) is estimated to be accordingly increased about two times. In otherwords, when a value of the threshold voltage Vth is beforehand set suchthat Vth<(Vdc/2) is satisfied, and even if the DC received voltage Vdcis increased about two times, the value of such an increased DC receivedvoltage Vdc is controlled to be lower than the element withstandingvoltage Vb (is avoided from exceeding the element withstanding voltageVb). For example, in the case where the element withstanding voltage Vbis 24 V, the threshold voltage Vth may be considered to be set to about10 V in consideration of a margin.

The value of the threshold voltage Vth may not be limited to a fixedvalue, and, for example, may be a variable value as below. Specifically,first, a voltage difference between the received voltage in thepreliminary power feeding and the received voltage in the main powerfeeding depends on the power to be received. This is because while thereceived voltage in the preliminary power feeding is constant regardlessof the power to be received, if the power to be received is high, thereceived voltage in the main power feeding is typically necessary tohave a large value. Consequently, for example, as illustrated by anarrow P2 in FIG. 14, the value of the threshold voltage Vth may be setto be variable depending on a level of the power to be received. Forexample, in the case where the element withstanding voltage Vb is 24 V,the value of the threshold voltage Vth may be considered to be set asbelow depending on a level of the power to be received (set to begradually decreased with an increase in power to be received).

-   -   In the case of power to be received≦5% . . . threshold voltage        Vth=14 V.    -   In the case of 5W<power to be received≦15% . . . threshold        voltage Vth=10 V.

(Switching from the half-bridge circuit to the full-bridge circuit isestimated.)

-   -   In the case of 15W<power to be received≦30% . . . threshold        voltage Vth=8 V.

(The received voltage in the main power feeding is estimated to beincreased two times or more from that in the preliminary power feeding.)

When the detected DC received voltage Vdc is determined to be lower thanthe threshold voltage Vth (Vdc<Vth) (step S105: Y), and even if theprocess is shifted to the subsequent main power feeding, so that the DCreceived voltage Vdc is increased about two times, the value of the DCreceived voltage Vdc does not exceed the element withstanding voltageVb. Specifically, in this case, the DC received voltage Vdc is notexcessively increased in the subsequent main power feeding (at a higherpower than the preliminary power feeding). In this case, therefore, thefollowing voltage reduction control is not performed, and the electronicunit 2 informs, using communication, the power feeding unit 1 of a startrequest of the main power feeding (step S106). Specifically, in thiscase, as illustrated in FIG. 7, each of the dummy loads Ra and Rb isstill set to be disconnected between the supply lines of the DC receivedvoltage Vdc (see a voltage range A1 indicated in FIG. 14).

On the other hand, when the detected DC received voltage Vdc isdetermined to be equal to or higher than the threshold voltage Vth(Vdc≧Vth) (step S105: N), the following voltage reduction control isperformed in the electronic unit 2.

Specifically, for example, as illustrated in FIG. 15, first, the controlsection 27 allows one or more (only the dummy load Ra in this exemplarycase) of the dummy loads Ra and Rb in the dummy load circuit 23 to beconnected between the supply lines of the DC received voltage Vdc (stepS107, see a voltage range A2 indicated in FIG. 14). Specifically, thecontrol section 27 controls the switching element SW2 a to be ON, andthe switching element SW2 b to be OFF. Consequently, as illustrated inFIG. 15, a current Ia flows through the dummy load Ra along the supplyline (power supply line Lp) of the DC received voltage Vdc, so that theDC received voltage Vdc is lowered. In this way, reduction control ofthe DC received voltage Vdc (voltage reduction control) is performed.

After such voltage reduction control is performed, the control section27 repeatedly determines whether the detected DC received voltage Vdc islower than the predetermined threshold voltage Vth (Vdc<Vth) or not(step S108). When the repeatedly detected DC received voltage Vdc isdetermined to be lower than the threshold voltage Vth (Vdc<Vth) (stepS108: Y), i.e., when the DC received voltage Vdc is decreased to lowerthan the threshold voltage Vth by the voltage reduction control, theprocess is shifted to step S106. Specifically, the electronic unit 2informs, using communication, the power feeding unit 1 of a startrequest of the main power feeding. This is because, in this case, the DCreceived voltage Vdc is also not excessively increased in the subsequentmain power feeding.

On the other hand, when the repeatedly detected DC received voltage Vdcis determined to be equal to or higher than the threshold voltage Vth(Vdc≧Vth) (step S108: N), i.e., when the DC received voltage Vdc isstill equal to or higher than the threshold voltage Vth after thevoltage reduction control is performed, the voltage reduction control isrepeatedly performed in the following manner. Specifically, the controlsection 27 allows a dummy load to be additionally connected between thesupply lines of the DC received voltage Vdc in the dummy load circuit23, or changes the dummy load to a dummy load having a larger load level(for example, a larger resistance value) (step S109). After suchrepeated voltage reduction control, the process is returned to stepS108.

When the control section 27 allows a dummy load to be additionallyconnected, for example, a configuration as illustrated in FIG. 16A isspecifically given. Specifically, in this exemplary case, the controlsection 27 allows not only the dummy load Ra but also the dummy loads Rbto be connected between the supply lines of the DC received voltage Vdc.More specifically, the control section 27 controls both the switchingelements SW2 a and SW2 b to be ON. Consequently, as illustrated in FIG.16A, currents Ia and Ib flow through the dummy loads Ra and Rb,respectively, along the supply line of the DC received voltage Vdc, sothat the DC received voltage Vdc is further lowered. In this way,further reduction control of the DC received voltage Vdc is performed.

On the other hand, when the control section 27 changes a dummy load to adummy load having a larger load level, for example, a configuration asillustrated in FIG. 16B is specifically given. Specifically, in thisexemplary case, when the dummy load Rb has a larger load level than thedummy load Ra, the control section 27 allows the dummy load Rb to beconnected between the supply lines of the DC received voltage Vdc inplace of the dummy load Ra. More specifically, the control section 27controls the switching element SW2 a to be OFF, and the switchingelement SW2 b to be ON. Consequently, as illustrated in FIG. 16B, thecurrent Ib flows through the dummy load Rb having a larger load levelalong the supply line of the DC received voltage Vdc, so that the DCreceived voltage Vdc is further decreased. In this way, furtherreduction control of the DC received voltage Vdc is performed.

After the power feeding unit 1 is informed of the start request of themain power feeding (step S106) as described above, the main powerfeeding at a higher power than the preliminary power feeding is startedfrom the power feeding unit 1 to the electronic unit 2 (step S110). Inother words, in the main power feeding, as described before, the ACsignal generation circuit 11 in the power feeding unit 1 is switchedfrom the half-bridge circuit to the full-bridge circuit.

When the main power feeding is started in this way, the control section27 sets the circuit such that the battery 25 as a main load is connectedto the power supply line Lp in the electronic unit 2 by switching thecharge section 24 into an operation state (step S111). Moreover, in stepS111, the control section 27 disconnects both the dummy loads Ra and Rbbetween the supply lines of the DC received voltage Vdc. Specifically,as illustrated in FIG. 7, the control section 27 controls both theswitching elements SW2 a and SW2 b to be OFF. Consequently, the currentsIa and Ib do not flow through the dummy loads Ra and Rb, respectively,and thus the reduction control of the DC received voltage Vdc isstopped.

Subsequently, in the electronic unit 2, the charge section 24 performsoperation of charging the battery 25 based on the received power(obtained through the main power feeding) (step S112). This is the endof the power feeding operation and charge operation illustrated in FIG.12.

As described above, in this embodiment, when the DC received voltage Vdcdetected during the preliminary power feeding from the power feedingunit 1 is equal to or higher than the threshold voltage Vth, the controlsection 27 performs the voltage reduction control so as to decrease theDC received voltage Vdc to lower than the threshold voltage Vth.Consequently, the DC received voltage Vdc is allowed to be avoided fromexcessively increasing during the subsequent main power feeding. Inother words, it is possible to prevent occurrence of overvoltage in theelectronic unit 2 due to the feeding voltage control in the powerfeeding unit 1. Consequently, it is possible to appropriately performcontrol during the power feeding using a magnetic field.

Moreover, since the element withstanding voltage Vb (such as a ratedwithstanding voltage, etc.) is allowed to be controlled to be low in theelectronic unit 2, for example, chip area and manufacturing cost of ICis allowed to be extremely reduced.

Furthermore, since the voltage reduction technique of this embodimentprevents the above-described occurrence of overvoltage unlike a safetydevice including, for example, a Zener diode, unstable operation isprevented in the electronic unit 2.

[Modifications]

Modifications (Modifications 1 and 2) of the above-described embodimentare now described. The same components as those in the above-describedembodiment are designated by the same numerals, and description of themis appropriately omitted.

[Modification 1]

FIG. 17 illustrates an exemplary relationship between a received voltage(DC received voltage Vdc) and a dummy load in Modification 1. InModification 1, a dummy load circuit 23 has a plurality of types (threetypes in this exemplary case) of dummy loads having different loadlevels (resistance values, etc.). When the DC received voltage Vdc isdetermined to be equal to or higher than the threshold voltage Vth, thecontrol section 27 allows a dummy load of a type, which is selected fromthe plurality of types of dummy loads in accordance with a level of thatDC received voltage Vdc, to be connected between the supply lines of theDC received voltage Vdc, and thus performs voltage reduction control.

Specifically, the control section 27 allows a dummy load having arelatively large load level to be connected between the supply lineswith an increase in DC received voltage Vdc. Specifically, in theexemplary case illustrated in FIG. 17, the control section 27 switches atype of the dummy load to be connected in order of “load: low”, “load:medium”, and “load: high” as a value of the DC received voltage Vdcincreases in a range of equal to or higher than the threshold voltageVth (i.e., with shift of a voltage range in order of a voltage rangeA21, a voltage range A22, and a voltage range A23).

Thus, in Modification 1, a dummy load of a type, which is selected fromthe plurality of types of dummy loads having different load levels inaccordance with a level of the detected DC received voltage Vdc, isallowed to be connected, making it possible to perform more precisevoltage reduction control.

Although three types of dummy loads having different load levels areused in the exemplary case illustrated in FIG. 17, two types or four ormore types of dummy loads may be used without limitation.

[Modification 2]

FIG. 18 is a block diagram as a circuit diagram illustrating anexemplary configuration of a power feeding system (power feeding system4A) according to Modification 2. The power feeding system 4A ofModification 2 corresponds to a modification of the power feeding system4 of the above-described embodiment, in which an electronic unit 2A isprovided as an objective unit of power feeding in place of theelectronic unit 2.

The electronic unit 2A is basically similar to the electronic unit 2except that the dummy load circuit 23 is not provided (is omitted), anda control section 27A is provided in place of the control section 27.

The control section 27A corresponds to a modification of the controlsection 27, which further has a function of controlling a load currentIL (a charge current flowing from the charge section 24 to the battery25 as a main load) with a control signal CTL3. Consequently, the controlsection 27A is allowed to perform reduction control of the receivedvoltage (DC received voltage Vdc) by controlling a level of the loadcurrent IL.

Specifically, when the DC received voltage Vdc is determined to be equalto or higher than the threshold voltage Vth, the control section 27Asets an appropriate load (corresponding to a dummy load) while holdingthe charge section 24 to be in an operation state, and thereby performscontrol such that a load current IL, which has a level high enough todecrease the DC received voltage Vdc, flows. When the DC receivedvoltage Vdc is decreased to lower than the threshold voltage Vth, thecontrol section 27A then resets the load current IL to an appropriatelevel. Such control of the load current IL also provides effects similarto those in the case of using the dummy loads in the above-describedembodiment.

In addition, the technique of Modification 3 allows effective use of acurrent unlike the case of using the dummy loads, and therefore makes itpossible to improve use efficiency of fed power.

[Other Modifications]

Although the technology according to the present disclosure has beendescribed with an example embodiment and Modifications thereofhereinbefore, the technology is not limited thereto, and variousmodifications or alterations thereof may be made.

For example, although the above-described embodiment and Modificationsthereof are described with various coils (the electricity transmissioncoil and the electricity reception coil), configurations (shapes) ofsuch coils may include any of various types. Specifically, the coil mayhave, for example, a spiral shape, a loop shape, a bar shape using amagnetic material, an α-round shape including a spiral coil that isdisposed in two layers in a folded manner, a spiral shape in three ormore layers, and a helical shape with a winding wound in a thicknessdirection. Each coil may be not only a winding coil configured of aconductive wire rod, but also a conductive pattern coil configured of aprinted circuit board or a flexible printed circuit board.

Although the above-described embodiment and Modifications thereof havebeen described with an electronic unit as an example of the objectiveunit of power feeding, the objective unit of power feeding is notlimited thereto, and may be a unit (for example, a vehicle such as anelectric car) other than the electronic unit.

Furthermore, although the above-described embodiment and Modificationsthereof have been described with the specific components of the powerfeeding unit and the electronic unit, all of the components may not befully provided. Also, other components may be further provided. Forexample, the power feeding unit or the electronic unit may incorporate acommunication function, a certain control function, a display function,an authentication function of a secondary unit, and a function ofdetecting contamination of a dissimilar metal, etc. Also, aconfiguration of the voltage reduction section (dummy load circuit) anda voltage reduction technique are not limited to those described in theabove-described embodiment and Modifications thereof, and otherconfiguration and techniques may be applicable. Specifically, the numberof dummy loads in the dummy load circuit is not limited to the number(two) described in the above-described embodiment and Modificationsthereof, and may be one or three or more.

In addition, although the above-described embodiment and Modificationsthereof have been described with an exemplary case where the voltagedetection section 22 detects the received voltage (DC received voltageVdc) that has been rectified by the rectifier circuit 21, this is notlimitative. Specifically, for example, a received voltage (an ACreceived voltage Vdc) that is still not rectified by the rectifiercircuit 21 may be detected and used for voltage reduction control.However, since the DC received voltage Vdc is more easily detected thanthe AC received voltage Vdc, the DC received voltage Vdc may bedesirably detected. Also, the position of the dummy load circuit 23 isnot limited to a position on a subsequent stage side of the rectifiercircuit 21 as in the above-described embodiment and Modificationsthereof, and, for example, may be a position on a preceding stage sideof the rectifier circuit 21.

Although the above-described embodiment and Modifications thereof havebeen described with an exemplary case where only one electronic unit isprovided in the power feeding system, the power feeding system is notlimited thereto, and a plurality of (two or more) electronic units maybe provided in the power feeding system.

Furthermore, although the above-described embodiment and Modificationsthereof have been described with a charge tray for a small electronicunit (CE unit) such as a mobile phone as an example of the power feedingunit, the power feeding unit is not limited to such a household chargetray, and may be applicable as a charger of any of various electronicunits. Moreover, the power feeding unit may not necessarily be a tray,and may be, for example, a stand for an electronic unit, such as aso-called cradle.

It is possible to achieve at least the following configurations from theabove-described example embodiments of the disclosure.

(1) An electronic unit, including:

an electricity reception section configured to receive power fed from apower feeding unit using a magnetic field;

a voltage detection section configured to detect a received voltagesupplied from the electricity reception section; and

a control section, wherein

while preliminary power feeding at a lower power than main power feedingis performed from the power feeding unit, and

when a received voltage detected by the voltage detection section isequal to or higher than a predetermined threshold voltage, the controlsection performs voltage reduction control so as to decrease thereceived voltage to lower than the threshold voltage.

(2) The electronic unit according to (1), further including:

a voltage reduction section including one or more dummy loads,

wherein the control section performs the voltage reduction control usingone or more of the dummy loads.

(3) The electronic unit according to (2), wherein

when the received voltage is equal to or higher than the thresholdvoltage, the control section allows one or more of the dummy loads to beconnected between supply lines of the received voltage so as to allow acurrent to flow through that dummy load, and thus performs the voltagereduction control.

(4) The electronic unit according to (3), wherein

when the main power feeding is started after the preliminary powerfeeding, and when a main load is then set to a connection state, thecontrol section disconnects the dummy load between the supply lines.

(5) The electronic unit according to (3) or (4), wherein

the voltage reduction section includes a plurality of types of the dummyloads having different load levels, and

when the received voltage is equal to or higher than the thresholdvoltage,

the control section allows a dummy load of a type, the type beingselected from the plurality of types of dummy loads in accordance with alevel of that received voltage, to be connected between the supplylines.

(6) The electronic unit according to (5), wherein the control sectionallows a dummy load having a relatively large load level to be connectedbetween the supply lines with an increase in the received voltage.(7) The electronic unit according to any one of (3) to (6), wherein

when one or more of the dummy loads has been connected between thesupply lines, and when the received voltage is still equal to or higherthan the threshold voltage,

the control section allows the dummy load to be additionally connectedbetween the supply lines, or changes the dummy load to a dummy loadhaving a larger load level.

(8) The electronic unit according to (1), wherein the control sectionperforms the voltage reduction control through controlling a level of aload current flowing through a main load.(9) The electronic unit according to any one of (1) to (8), wherein whenthe received voltage has been decreased to lower than the thresholdvoltage, the control section informs the power feeding unit of a startrequest of the main power feeding.(10) The electronic unit according to (9), wherein

when the power feeding unit has started the main power feeding,

the control section sets a secondary battery as a main load to aconnection state, and allows start of operation of charging thesecondary battery based on the main power feeding.

(11) The electronic unit according to any one of (1) to (10), whereinthe threshold voltage is set to a value less than half the value of anelement withstanding voltage in the electronic unit.(12) The electronic unit according to any one of (1) to (11), wherein avalue of the threshold voltage is varied in accordance with a level ofreceived power received by the electricity reception section.(13) The electronic unit according to any one of (1) to (12), furtherincluding:

a rectifier circuit configured to rectify the received voltage,

wherein the voltage detection section detects the received voltage thathas been rectified by the rectifier circuit.

(14) A power feeding system, including:

one or more electronic units; and

a power feeding unit configured to perform power feeding to theelectronic unit using a magnetic field,

wherein the electronic unit includes

an electricity reception section that receives power fed from the powerfeeding unit,

a voltage detection section that detects a received voltage suppliedfrom the electricity reception section, and

a control section, wherein

while preliminary power feeding at a lower power than main power feedingis performed from the power feeding unit, and

when a received voltage detected by the voltage detection section isequal to or higher than a predetermined threshold voltage, the controlsection performs voltage reduction control so as to decrease thereceived voltage to lower than the threshold voltage.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. An electronic unit, comprising: an electricity reception section configured to receive power fed from a power feeding unit using a magnetic field; a voltage detection section configured to detect a received voltage supplied from the electricity reception section; and a control section, wherein while preliminary power feeding at a lower power than main power feeding is performed from the power feeding unit, and when a received voltage detected by the voltage detection section is equal to or higher than a predetermined threshold voltage, the control section performs voltage reduction control so as to decrease the received voltage to lower than the threshold voltage.
 2. The electronic unit according to claim 1, further comprising: a voltage reduction section including one or more dummy loads, wherein the control section performs the voltage reduction control using one or more of the dummy loads.
 3. The electronic unit according to claim 2, wherein when the received voltage is equal to or higher than the threshold voltage, the control section allows one or more of the dummy loads to be connected between supply lines of the received voltage so as to allow a current to flow through that dummy load, and thus performs the voltage reduction control.
 4. The electronic unit according to claim 3, wherein when the main power feeding is started after the preliminary power feeding, and when a main load is then set to a connection state, the control section disconnects the dummy load between the supply lines.
 5. The electronic unit according to claim 3, wherein the voltage reduction section includes a plurality of types of the dummy loads having different load levels, and when the received voltage is equal to or higher than the threshold voltage, the control section allows a dummy load of a type, the type being selected from the plurality of types of dummy loads in accordance with a level of that received voltage, to be connected between the supply lines.
 6. The electronic unit according to claim 5, wherein the control section allows a dummy load having a relatively large load level to be connected between the supply lines with an increase in the received voltage.
 7. The electronic unit according to claim 3, wherein when one or more of the dummy loads has been connected between the supply lines, and when the received voltage is still equal to or higher than the threshold voltage, the control section allows the dummy load to be additionally connected between the supply lines, or changes the dummy load to a dummy load having a larger load level.
 8. The electronic unit according to claim 1, wherein the control section performs the voltage reduction control through controlling a level of a load current flowing through a main load.
 9. The electronic unit according to claim 1, wherein when the received voltage has been decreased to lower than the threshold voltage, the control section informs the power feeding unit of a start request of the main power feeding.
 10. The electronic unit according to claim 9, wherein when the power feeding unit has started the main power feeding, the control section sets a secondary battery as a main load to a connection state, and allows start of operation of charging the secondary battery based on the main power feeding.
 11. The electronic unit according to claim 1, wherein the threshold voltage is set to a value less than half the value of an element withstanding voltage in the electronic unit.
 12. The electronic unit according to claim 1, wherein a value of the threshold voltage is varied in accordance with a level of received power received by the electricity reception section.
 13. The electronic unit according to claim 1, further comprising: a rectifier circuit configured to rectify the received voltage, wherein the voltage detection section detects the received voltage that has been rectified by the rectifier circuit.
 14. A power feeding system, comprising: one or more electronic units; and a power feeding unit configured to perform power feeding to the electronic unit using a magnetic field, wherein the electronic unit includes an electricity reception section that receives power fed from the power feeding unit, a voltage detection section that detects a received voltage supplied from the electricity reception section, and a control section, wherein while preliminary power feeding at a lower power than main power feeding is performed from the power feeding unit, and when a received voltage detected by the voltage detection section is equal to or higher than a predetermined threshold voltage, the control section performs voltage reduction control so as to decrease the received voltage to lower than the threshold voltage. 